[citation needed] To another person, the way an individual behaves and speaks reflects their true inner self and can be used to gain insight into who they really are.
[citation needed] Aristotle, following Plato, defined the psyche as the core essence of a living being, and while claiming that it did not exist apart from the body,[2] he considered its so-called "intellect" part to be immortal and perpetual,[3][4] in contrast to its organism-dependent vegetative/nutritive and perceptual functions.
He states: "Soul is an actuality or formulable essence of something that possesses a potentiality of being besouled",[5][6] and also "When mind is set free from its present conditions it appears as just what it is and nothing more: this alone is immortal and eternal".
[9]While he was imprisoned in a castle, Avicenna wrote his famous "floating man" thought experiment to demonstrate human self-awareness and the substantiality of the soul.
His thought experiment tells its readers to imagine themselves suspended in the air, isolated from all sensations, which includes no sensory contact with even their own bodies.
He thus concludes that the idea of the self is not dependent on any physical thing, and that the soul should not be seen in relative terms, but as a primary given, a substance.
Rather, Hume compares the soul to a commonwealth, which retains its identity not by virtue of some enduring core substance, but by being composed of many different, related, and yet constantly changing elements.
[14] The spiritual goal of many traditions involves the dissolving of the ego, in contrast to the essential Self,[15] allowing self-knowledge of one's own true nature to become experienced and enacted in the world.
[citation needed] Hume's position is similar to Indian Buddhists’ theories and debates about the self, which generally considers a bundle theory to describe the mind phenomena grouped in aggregates (skandhas), such as sense-perceptions, intellective discrimination (saṃjñā), emotions and volition.
Since the beginning of Buddhist philosophy, several schools of interpretation assumed that a self cannot be identified with the transient aggregates, as they are non-self, but some traditions questioned further whether there can be an unchanging ground which defines a real and permanent individual identity, sustaining the impermanent phenomena; concepts such as Buddha-nature are found in the Mahayana lineage, and of an ultimate reality in dzogchen tradition, for instance in Dolpopa[16] and Longchenpa.
That absence of a self definition is directed to avoid clinging to the "I", seek reality and attain detachment,[19] and it is found in many passages of the oldest Buddha sutras, recorded in the Pali Canon, such as this:"Bhikkhus, form is not-self.
"[20]Both Western and Eastern civilizations have been occupied with self-knowledge and underscored its importance particularly citing the paradoxical combination of immediate availability and profound obscurity involved in its pursuit.
"[22] The case is the same for the seers of Upanishads, who maintained that the ultimate real knowledge involves an understanding of the essence of the self and the nature of God.
"[26] A theory about self-knowledge describes the concept as the capacity to detect that the sensations, thoughts, mental states, and attitudes as one's own.
[27] This school rejects that self-knowledge is merely derived from observation as it acknowledges the subject as authoritative on account of his ability as an agent to shape his own states.